1. Field of the Invention
The present invention relates generally to a method of manufacturing a Group III nitride crystal substrate, an etchant to be used in the method, a Group III nitride crystal substrate, and a semiconductor device with the same.
2. Related Background Art
A Group III nitride compound semiconductor such as, for instance, gallium nitride (GaN) (hereinafter also referred to as a “Group III nitride semiconductor” or a “GaN-based semiconductor”) has been gaining attention as a material for semiconductor devices that emit green, blue or ultraviolet light. A laser diode (LD) that emits blue light is used for high-density optical disk devices or displays while a light emitting diode (LED) that emits blue light is used for displays, lighting, etc. It is expected to use an ultraviolet LD in the field of, for example, biotechnology and an ultraviolet LED as, for example, an ultraviolet source for a fluorescent lamp.
Generally, Group III nitride semiconductor substrates (for instance, GaN substrates) that are used for LDs or LEDs are formed through vapor phase growth.
Recently, template substrates and free-standing bulk substrates have been studied as substrates to be used for semiconductor devices such as the above-mentioned LDs and LEDs. The template substrates are grown on various support substrates by a metalorganic chemical vapor deposition (MOCVD) method or hydrid vapor phase epitaxy (HVPE), while the free-standing bulk substrates are obtained by removing the support substrates after growth. Further, another method of growing a GaN crystal layer on a sapphire substrate by the MOCVD method and then growing single crystals thereon by a liquid phase epitaxy (LPE) method has been reported (see, for instance, JP2002-293696A and Japanese Association for Crystal Growth, Vol. 30, No. 2, pp. 96–103, 2003).
Furthermore, various methods for processing substrates also have been proposed (see, for instance, Appl. Phys. Let. (Vol. 68, No. 7, pp. 917–919, 1996) and Solid-state Electronics. (Vol.41, No. 2, pp. 295–298, 1997)).
Immediately after crystal growth, the surface of a Group III nitride crystal substrate has, for instance, a large number of small holes (pits), concavities and convexities (hillocks), and natural planes that are referred to as facets. Hence, when such a Group III nitride crystal substrate is used to manufacture a product such as a semiconductor device, it is necessary to process the surface of the substrate beforehand. The Group III nitride crystal substrate, however, is hard and brittle and therefore is difficult to process.